1. Field of the Invention
The invention relates to a device for producing a pourable product, in particular a pourable product with a coating. The device includes a guide vane. The invention further relates to various methods for using the device.
A pourable product is understood to be the finished product in the respective application of the invention. In this case, the pourable product may be composed basically of the same or different starting materials with a radially homogeneous or layered structure.
The pourable product may be of any kind, insofar as it is possible to put both this and the respective starting materials into radially peripheral circulation.
2. Description of Related Art
According to the prior art, various methods and devices for the granulation of starting materials or the coating of cores are known.
DE 41 28 258 A1 specifies a method for the uniform closed coating of grains, such as seed grains, by means of a rotor granulator with integrated fluidized-bed drying and a device for carrying it out. According to the method, the batch circulated by the running rotor and containing the dissolved or suspended coating materials is sprayed through one or more nozzles arranged in the free inner space of the stator and assisted by compressed air, warm air being introduced through the annular gap between the rotor and stator into the space containing the circulated batch. The associated device specifies a rotor, the cross section of which decreases from the center at an angle of up to 45xc2x0 to the plane and is curved upward at the outer circumference, with a radius of about 10 to 20% of its diameter, to an edge angle of 45xc2x0. Located above the rotor in the stator, the deflecting funnel, is a thin-walled rotationally symmetric annular screen surface or annular gap surface which is surrounded on the outside by an air duct.
DE 4411058 C2 specifies a device for the coating of granular material, in particular for the coating of seed with chemicals, such as dressing agents. The device has a conically upwardly widened side wall of a mixing cylinder which rotates at high speed and which is rotatable about a vertical axis. The liquid chemicals are sprayed via a spraying means onto the granular material located in the mixing cylinder. For better intermixing of the granular material in the mixing chamber, bent diverting blades are arranged above the mixing cylinder on a discharge ring, said diverting blades deflecting the material and leading it back downward into the conical mixing cylinder.
The solutions according to the prior art often have relatively low productivity or can be used only to a limited extent for coatings. For example, the diverting blades engage into the material, and delicate products or their coatings, for example in the form of a pasty enveloping layer, are destroyed.
The object on which the invention is based is to specify a device for producing a pourable product, in particular a pourable product with a delicate structure or coating, of the type initially mentioned, which ensures high quality and productivity at a relatively low technical outlay. The invention relates, furthermore, to two methods for using the device.
Starting materials within the meaning of the invention are to be understood basically as all materials which are introduced into the device. These may be pulverulent materials, from which basic cores in the form of a granulate are produced, particularly in cooperation with a binder. In one use of the device, an enveloping layer consisting of the same or different starting materials can be built up on these basic cores or any other cores.
The xe2x80x9cotherxe2x80x9d cores which may be coated are, for example, granulates, pellets, grains, seed grains, tablets, pills and the like. In this case, the cores may be homogeneous or an agglomerate or a core which has already been coated previously with one or more layers.
A coating is a layer which is built up or precipitated on a core in such a way that the core is surrounded essentially uniformly.
The coating may be composed of a material, a liquid or dispersion or of a mixture of a plurality of materials, for example of a conglomeration (snowball effect) of a pulverulent starting material and a liquid binder. The pulverulent starting material may, in this case, be a homogeneous material or mixture of a plurality of materials. It is often a neutral material which serves merely, in conglomeration with the liquid binder, for enveloping the core and at the same time giving the product as uniform a shape as possible with the same dimensions. Both the pulverulent starting material and the binder may also contain active substances intended for the envisaged use.
In order to simplify the remaining description of the invention, both the basic cores and the xe2x80x9cotherxe2x80x9d independent cores are designated below, in general, only as cores, and starting materials are to be understood accordingly as the starting materials which are introduced into the device in order to form the basic cores or to apply an enveloping layer to existing cores.
An important aspect of the invention is that the starting materials, in particular the cores used, and ultimately the finished pourable product itself are put into a specific circulating movement by the rotor.
The starting materials or the cores are put by the rotor into a radially tangential direction of movement which is changed to a vertically tangential direction in the outer region of the rotor and in the vicinity of the wall of the rotor chamber.
Consequently, the cores leave the active region of the rotor with a kinetic energy which is sufficient for the cores to roll along on the guide vanes arranged statically on the rotor chamber and, at the same time, to change their direction of movement positively according to the shape of the guide vanes and essentially be deflected and fall back into the rotor.
The radially tangential direction of movement of the cores is inclined upward, at least in the radially outer third of the rotor, at an angle of between 10xc2x0 and 80xc2x0 to the axis of rotation, until the cores on the wall of the rotor chamber leave the rotor upward in a vertically tangential direction with kinetic energy. The inclination, which is advantageous in practice, is determined in each case by the mass of the cores or of the pourable products in conjunction with the diameter of the rotor and the rotational speed of the latter.
The cores are put, as a whole, into specific intensive, essentially concussion-free circulation, in which the cores and, in particular, the enveloping layers growing on the cores are not exposed to any adverse compressive and concussive loads.
According to the invention, the guide vanes are arranged statically on the inner wall of the rotor chamber above the plane of the upper edge of the rotor. In cross section relative to the rotor axis, they have essentially the shape of a segment of a circle or of a spiral. The outer ends of the segments emerge from the circle of the inner wall of the rotor chamber in the direction of rotation of the rotor, the tangents of the inner wall and of the guide vanes at the contact point having essentially the same inclination. The inner ends of the segments lie approximately in the middle part of the rotor radius.
By virtue of this specific configuration, the circulating product, in particular with delicate enveloping layers, can roll on the rotor, essentially free of concussion, under the influence of the kinetic energy, leave said rotor and roll on the inside of the guide vanes until it falls back into the rotor.
The cores do not, in particular, impinge onto angular fittings, for example on circulation obstacles, such as are used according to the prior art.
The cores roll intensively and uniformly on the guide vanes and against one another, so that they are exposed essentially on all sides to identical compressive loads and a uniform coating is formed.
Where thicker enveloping layers are used as a coating, it may also be advantageous to vary the guide vanes specifically as a function of the rollability of the cores, so that the cores are put into advantageous circulation according to their mass and size. For example, the vertical surfaces of the guide vanes may be arranged at least partially so as to be inclined to the perpendicular.
In one embodiment, the shape of the circular or spiral segments of the guide vanes may also be varied by an adjusting means. For this purpose, the guide vanes may be multiply divided. In the case of adjustment, individual or all parts of the guide vanes are then varied relative to one another in such a way that a different overall shape of the circular or spiral segments is formed.
By means of a device of this kind, in the event of a variation in the mass, the rolling movement of the coated cores or products can be optimized in a highly advantageous way.
At the beginning of the production of basic cores or a coating, the individual elements of the starting materials have substantially lower masses than at the end of the production of a pourable product. The specific rolling conditions therefore also change. By a change in the geometry of the guide vanes, also in conjunction with a change in the rotational speed of the rotor, an optimum rolling movement can be brought about in a highly advantageous way. A device with such a design may also advantageously be used as a universal plant for the selective production of widely varying pourable products.
The feed of different starting materials, for example of a pulverulent starting material and/or a liquid binder, to the circulating cores is carried out, basically, in a coordinated regime. The starting materials are metered in such a way that, immediately after the feed, they build up directly as an enveloping layer on the cores. The liquid binder moistens the cores or the surface of the partly coated cores and the pulverulent starting material then adheres to this moist surface. This ensures that no agglomerates of the starting materials for the enveloping layer can be formed without a core.
If basic cores are to be produced, generally in a first step, the management of the method depends greatly on the starting material. On the one hand, it may be possible for the starting material to be granulated or pilled solely as a result of the rolling movement. As a rule, however, a negligible quantity of binder, for example water, is added to a powder, so that the basic cores form around the drops of the binder. As a result, further starting material can then be applied to the basic cores in the manner of a coating.
If it is advantageous, in terms of the method, to dry the pourable product during and/or after coating, sheet-like gas passages in the form of perforations or screens may be arranged at least partially in the cone shell. A dry gas can be led from below through the gas passages via suitable feed devices.
The dry gas consequently flows around the cores very effectively and virtually at every point. The type of dry gas, its flow velocity and its temperature are influenced critically by the specific conditions of the respective products.
In principle, the device according to the invention is designed as a batch-fed plant, since the production of the pourable products requires the effect of the specific circulation for a certain amount of time. It is also possible, however, to operate the device as an interval flow plant. That is to say, the starting materials or the cores and the starting materials for building up the enveloping layer on them are fed to the rotor chamber at intervals and, after an appropriate process duration, are discharged from the latter again.
A solution which has proved appropriate for discharging the product from the device is one in which at least one flap is located in the wall of the rotor chamber above the rotor and preferably within a guide vane, said flap being suitable for moving the products out of the rotor chamber by means of the centrifugal forces when the flap is in the open position and when the rotor is rotating.
It is also possible, for example, for the finished product to be sucked away by means of a suction tube introduced into the rotor chamber from above.
The advantage of the invention is, in particular, that pourable products of widely varying kinds can be produced highly effectively, undried or dried, in a simple and careful way.
The production of the pourable products, with regard to both production of simple granulates and to the build up of complicated and delicate enveloping layers, by means of the device according to the invention leads to a product with a surprisingly uniform external shape. Depending on the shape of the cores and on the selected thickness of the enveloping layer, the products have a spherical shape or a shape diverging from this. If, for example, elongate cores are coated, then the product becomes spherical only when a relatively thick enveloping layer is applied. If this is not desirable, then, with a smaller thickness of the enveloping layer, the product will also still have an elongate shape.
It is particularly advantageous that any pronounced concussive or compressive load on the individual product particles is avoided when the device according to the invention is used. Consequently, where partly coated cores are concerned, there is also no coating material knocked off in a way which is usually highly disadvantageous. Such destructions of partly coated cores occur in the prior art, for example, due to the fact that the guide devices engage with their edges into the circulating material. The knocked-off coating materials may therefore form a separate granulate without a core. Such a granulate is harmful or disadvantageous when the core has a particular function, for example as a seed grain. During sowing, a defect occurs, entailing a corresponding crop loss.
The invention will be explained in more detail below with reference to two exemplary embodiments.